So it’s no surprise that the nose would interpret tellurium and sulfur compounds in similar ways. The smell is so overwhelming that according to legend, a few researchers have been driven to suicide.) The Rockefeller study revealed that the presence of sulfur atoms is strongly associated with garlic smells, and tellurium sits just two spots below sulfur on the periodic table. (Chemists exposed to tellurium often reek like garlic for weeks or even months afterward. The garlic prediction is especially interesting for periodic table buffs since it explains one of the table’s great mysteries-why tellurium, element 52, smells like the most pungent garlic on Earth. The 19 broad descriptions of odors also fell into two clusters: those hard to guess (wood, urinous, musky) and those easy to guess (fruit, spices, burnt, garlic). The hardest molecules to predict included L-cysteine, which smells somewhat like rotten eggs. When it came to matching odors to structures, the computers had the easiest time predicting the smell of 3-methyl-cyclohexanone (a camphor-like odor) and ethyl heptanoate (sweet grape). Having polar groups within the molecule (regions of strong positive or negative charge), such as phenols, enols, and carboxyls, also ratcheted up the smell’s intensity. Small molecules, for instance, tended to produce much more intense smells than large ones. The Rockefeller researchers then gathered input from all the teams to further investigate the chemical nature of smell.Ī few trends became clear immediately. Eighteen teams accepted the challenge, with groups from the University of Michigan and Arizona State University developing the most accurate algorithms. In this case the Rockefeller team challenged computer geeks to find correlations in their data between odor and chemical structure. The DREAM Challenges website promotes cooperation between biology and computer science by suggesting topics that might lend themselves well to computer analysis.
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The scientists also mapped out the chemical geometry of all the molecules, including the identity of every atom within them.Īs a next step the researchers turned to an unlikely source for help: artificial intelligence. The subjects ranked the intensity and pleasantness of each, then classified the scents using 19 descriptors, including fish, sour, sweaty, bakery, and decayed. The study began when sensory scientists at Rockefeller University recruited 49 volunteers to rate the smells of 476 chemicals. But thanks to an innovative new study, scientists have finally gotten some traction on olfaction, allowing them to match specific chemical features to specific odors for the first time. Similarly shaped molecules can have quite different odors, and molecules that look nothing alike can smell almost the same. The reason for this remains obscure, but the setup gives odors an uncanny power to unlock hidden memories.
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Unlike other senses smell is wired directly to the emotional centers in our brain. There’s no sense so intimate-or mysterious-as smell.